Volcanoes:

itle/volcano_natures_inferno Watch this national Geografic documentary on volcanos.

A. What is A Volcano ? 1. An opening in Earth’s crust through which molten rock, ash and gases erupt. 2.Volcano: The landform that develops around the opening. 3. A way for Earth to release heat energy from the interior due to radioactive decay. D. Peebles

B. Types of Volcanoes? 1. Composite2. Shield 3. Cinder A. Heisey G. Vaughn USGS Mt. St. Helens, WAMauna Loa, HW Sunset Crater, AZ

C. How Do Volcanoes Differ? 1. Size 2. Shape 3. Composition 4. Location Tarbuck & Lutgens

Questions Which type of volcano is the widest? A. Cinder B. Composite C. Shield What type of volcano typically produces the largest explosions? A. CinderB. CompositeC. Shield

D. Composition 1. Magma viscosity –Silica content: more = thicker (most explosive) –Temperature: higher= thinner –High Viscosity = thick, pasty –Low viscosity= Thin and runny 2. Mafic –Little silica –low viscosity (runny) –Produces Dark color rocks –Ex.Basalt 3. Felsic -Silica rich -High viscosity -Light color rocks -Granite -Explosive, high gas content 4. Pyroclastic- Fire Rock. What comes out of the volcano Explosive volcanic events. D. Peebles, USGS D. Weintraub Kilauea, HW Mt. St. Helens, WA

Questions 3 Which variable determines how explosive a volcanic eruption will be? A. GasesB. Silica C. Temperature

E. Types of Lava Flow 1. Flow types: depend on temperature and comp. –Pahoehoe: fast moving, hot lava, low viscosity –Aa Aa: slower moving, cooler, higher viscosity D. Peebles, USGS J. Judd, USGS J.D. Griggs, USGS Aa Flow J.D. Griggs, USGS Pahoehoe Flow com/watch?v=iyIV5f d1Aww om/watch?v=Z9iW_o XMBB8

F. Shield Volcanoes 1. Mafic lava (fluid) –nonexplosive eruptions, slow build up –Hot spots and ridges (mantle material) 2. Structure –Low angle slope Why ? Because the lava can travel long distances due to its fluidity. Low gas content!! Tarbuck & Lutgens

Questions Shield volcanoes are composed of what type of lavas? A.Mafic B. FelsicC. Andesitic The shape of a shield volcano is due to A. fluid, low viscosity lavas B. high viscosity lavas C. pyroclastics D. gases Shield volcanoes are usually associated with what landform feature/s or processes? A. pyroclastic flows B. explosive eruptions C. steep sided conesD. Gentle sloped cones

G. Cinder Cones 1. Mafic lavas (can be felsic) –Large amt. pyroclastics –Gentle & explosive –High viscosity 2. Structure –High slope 3. Deep crater A. Heisey Tarbuck & Lutgens

Example: Paricutin West of Mexico City 1943 eruption began Cornfield of Dionisio Pulido Earthquakes 1 st day 130 feet 5 th day +330 feet Lava flows from base Nine years of eruption T. Nichols

Cinder Cones USGS G. Lewis Fire Fountain=Pyroclastics Parasitic Cone Pelee’s Cinder Cone, HW

Question Cinder cones are mainly composed of -?- lavas A.Mafic B. Felsic C. Andesitic

I. Composite Volcanoes Felsic lavas –Large amt. pyroclastics –Viscous lavas –Explosive / catastrophic eruptions –Subduction boundaries Structure –Symmetrical cone –Medium to high slope Ring of Fire M. Giannechini Pomerape & Parinacota, Chile

Cascade Range 50+ eruptions in U.S. in past 200 years (mainly in Alaska) Pyroclastic Flows Lahars USGS Pre 1980 EruptionPost 1980 Eruption

Questions Composite volcanoes are composed of -?- lavas A.Mafic B. Felsic C. Andesitic The volcano with the steepest slope is a A.Shield cone B. Cinder cone C. Composite cone Volcanoes of the Cascade Range are mainly A.Shield B. Cinder C. Composite

Where are Volcanoes Located? Tarbuck & Luntguns UNAVCO

K. Volcanoes Locations 1.Located along plate boundaries 2.“Ring of Fire”- major volcanic belt, formed around the Pacific Ocean.

3. Hot spots-stationary plume of magma continually rising through the crust from the athenosphere. Can occur in the middle of a plate.

Check it out! Looking at the current location of the Yellowstone hot spot 1. If hot spots never move in which direction is the north American continent moving?

West, south west!

Bell Ringer. In your comp book draw a data table using a ruler, showing the following, Size, shape, composition, and Eruption type. Do this for the 3 types of volcanoes.

Other Volcanic Features Lava Plateaus J. Shelton D. Falconer T. Bean Lava Dome Volcanic Neck Rift Eruption G. Vaughn

K. Other Volcanic Structures 1. Plateaus- flat area caused by lava flow. 2. Volcanic necks- magma left in vent, extinct volcano 3. Dikes- molten material that vertically cut across rock layers 4. Sill- molten material that horizontally cut across rock layers Tarbuck & Luntgens

4. Laccoliths- domelike magma bulge under the surface. 5. Batholiths- large rock structure, magma cools inside crust 6. Active- erupting or will erupt soon. 7. Dormant- erupt in the future. 8. extinct- unlikely to erupt again

Check Your Volcano Knowledge What purpose do volcanoes serve on Earth? What is magma? List three factors that determine the nature of a volcanic eruption. What are the major gases released in volcanic eruptions? What does Pahoehoe and Aa refer to? What are the three types of volcanoes? Describe each one. What type of materials make up pyroclastic flows? Generally, where are volcanoes located on Earth? How does a caldera form? What are Lahars and what type of volcano are they usually associated with? Which type of volcano is the most explosive? Name and describe three other igneous features.

J. Calderas USGS G. Lewis Crater Lake, OR Long Valley, CA Mauna Loa, HW 1. Huge hole left by the collapse of a whole mountain.